Electrically heated screen for separating coarser material from accompanying fines



M y 1951 J. KUFFERATH 2,984,357

ELECTRICALLY HEATED SCREEN FOR SEPARATING COARSER MATERIAL FROM COMPANYING FINES Filed June 1957 INVENTOR.

United States Patent ELECTRICALLY HEATED SCREEN FOR SEPARAT- ING COARSER MATERIAL FROM ACCOMPANY- ING FINES Josef Kuflerath, Mariaweiler, near Duren, Germany Filed June 25, 1957, Ser. No. 667,863

Claims priority, application Germany Apr. 8, 1957 2 Claims. (Cl. 209-401) This invention relates to electrically heated screens, and more particularly to Woven wire screens or screen cloths, for the separation of coarser material from accompanying fines. By fines, undersize material is meant that passes through the screen cloth.

It is known to heat screens for the removal of the finest particles from wet coal and the like by passing electric current through the screen. Heating is intended to reduce clogging of such screens. It is customary to use for this purpose plates provided with suitably fine perforations. The manufacture of these plates, however, is relatively costly. In order to obtain reasonable plate life, it is necessary to employ plates of adequate thickness which are heavy and expensive. Yet, the most important difficulties are encountered in the practical application of such screens. The total clear area is only about of the screen surface. The capacity is correspondingly low. Extremely heavy currents are required to maintain the plate during operation at a temperature of to 70 C. At an applied potential of 7 volts, for example, a current of 1,200 amps. resulted. It is a most serious disadvantage of this type of screen that the fine perforations, despite heating, will again become clogged. The dust-removal plant has to be stopped approximately every two hours and the screen must be cleaned by brushes or other means. During the two-hour runs, the efiiciency, of course, drops gradually.

It has also been tried to use instead of the referred to punched plates woven wire screens made of round wires. Such screens did not give satisfactory results either. The surface blinds in a very short time so that the screening operation must again and again be interrupted.

The present invention aims at electrically heated woven wire screens for the separation of coarser material from accompanying fines, which will be free of the disadvantages of screening mediums suggested and used heretofore. Other objects of my invention will appear from the following description.

In accordance with the invention, its objects are achieved by providing a wire cloth which is made up by warp and filling wires, and in which the warp and/or filling wires have their greatest width near the top surface of the screen.

My present invention provides that the warp and/or filling wires, when viewed in cross section, have a top, with the remainder of the outline being curved, that is, not angular or pointed. A fiat top was found satisfactory. The remainder of the outline may be formed like the arc of a circle. Good results were obtained with semicircular wires.

I prefer wires of a cross section in the shape of a segment of a circle, the segment having a height of approximately of the width of the wire. Most satisfactory results were obtained with woven wire screens, the wires of which have a height of approximately 0.6 mm., a width of 0.8 mm., and define openings having an unobstructed width of approximately 1.5 mm.

2,984,357 Patented May 16, 1951 My wire screen is preferably made of a rust-resistant steel.

It is evident that the dimensions of the wire and aperture may vary, depending on the undersize material which is to be sepaarted and has to pass through the screen cloth.

The smallest section of the openings in the screen of the present invention is located near the top surface of the screen. Grains of the material, which are of such a size as to enter partially into the openings without passing therethrough cannot cause permanent clogging. They are either wiped off by the material subsequently passing over the screen, or pressed through the openings while being partially comminuted. Nor is it possible for several smaller particles to stick together and to form a bridge between the walls of the openings. Once a particle has passed through the narrow portion, near the top surface, of an opening, no clogging can occur in the remainder of the passage since the individual openings widen more or less toward the underside of the screen.

A screen for separation of coarser material from accompanying fines, according to the invention, has a clear area of 40-60%. This results in a substantial increase in capacity, as compared with the punched plates commonly used until now. In the specific example referred to hereinbefore, a current of 200 amperes is adequate for heating. With the elimination of periodic stoppages for the cleaning of the screen which is automatically purged by the material being sieved, the overall capacity may be increased up to twice or three times the normal capacity of conventional equipment of equal overall size.

Use of rust-resistant steel wires eliminates corrosion so that the useful life of the screen of the invention is substantially longer than that of punched plate-screens so far commonly used for the removal of dust and fines.

The screen may be provided with square openings and may be woven in a basket weave. It is also possible to use other than square-mesh woven wire screens, for instance, screens with longitudinal or transverse rectangular or slot openings. Weaves with more than one wire being interlaced may also be used, for instance, a twill weave with three, four or five wires being passed over or under, or a multiple wire satin weave.

In order that the present invention may be fully understood, illustrative embodiments are hereinafter described, by way of example, and shown in the accompanying drawing forming a part hereof and wherein:

Fig. l is a fragmentary perspective view of a wire cloth embodying the present invention, drawn to enlarged scale when compared with the scale of Fig. 3;

Fig. 2 is a cross section through a wire as used according to the invention, drawn to a more enlarged scale; and

Fig. 3 is explanatory of the mounting of a screen.

Referring to the drawing in detail, and initially to Figs. 1 and 2, in the wire cloth or screen shown in Fig. l and generally designated S, the wires 10 and 11 interlace alternately. The wires are of rust-resistant steel and have a cross section, the shape of which conforms to the segment of a circle. The segmental area is bounded by an are 14 and a chord 15. The height 12 of the arc is approximately of the diameter 13 of the wire. The chord 15 being a straight line, the top surface 15' of the wires is flat. The remaining surface 14 of the wires is of cylindrical shape. The greatest width of the wires is near the top surface of the screen.

In Fig. 3, the screen 8 is shown to be conductively secured at its edge portions 16' to a frame 18. Two lugs 20 secured to respective opposite edge portions 16 are connected to the two poles of a source of voltage for passing heating current through the screen. In order to ensure a reliable contact under all circumstances and to distribute the current flow uniformly over the screen area between the lugs 20, the edge portions 16 are filled with tin 22 or like conducting material.

It is believed that the screen of my invention and the many advantages thereof will be fully understood from the foregoing description, and it will beapparent that while I have shown and described my invention in a number of forms only, many changes and modifications may be made without departing from the spirit of the invention defined in the following claims.

What is claimed is:

1. In a screen for the separation of coarser material from accompanying fines, said screen having openings of predetermined size for the passage therethrough of said fines from the top surface to the bottom surface of said screen while said coarser material is retained on the top surface of said screen, a screen cloth comprising, in combination, a first group of spaced wires extending substantially in a common plane in one direction; and a second group of spaced wires extending substantially in said plane in another direction transverse of said one direction, said wires therebetween defining the openings of said screen, the wires of at least one of said groups having a cross section defined by a substantially circular arc and a chord of said are so that each wire has a fiat surface portion and a substantially cylindrically curved surface portion, the wires of said one group being arranged in said screen cloth in such a manner that the flat surface portions thereof are located in the top surface of said screen, and the curved surface portions thereof are at least partly located in the bottom surface of said screen, whereby each of said openings has a pair of opposite walls formed by two adjacent Wires of said one group, said walls being closest spaced from each other adjacent said top surface, and diverging from the area of closest spacing toward said bottom surface.

2. In a screen for the separation of coarser material from accompanying fines, said screen having openings of predetermined size for the passage therethrough of said fines from the top surface to the bottom surface of said screen while said coarser material is retained on the top surface of the screen, a woven screen cloth, comprising, in combination, a first group of spaced wires extending substantially in a common plane in one direction; a second group of spaced wires interlaced with said first group and extending substantially in said plane in another direction transverse of said one direction, said wires therebetween defining the openings of said screen, the wires of at least one of said groups having a substantially uniform segmentshaped cross section defined by a substantially circular arc and a chord of saidarc, the height of the segment perpendicular to the chord being substantially not more than three quarters of the diameter of the circle, so that each wire has a flat surface portion and a substantially cylindrical curved surface portion, the wires of said one group being arranged in said screen cloth in such a manner that the flat surface portions thereof are located substantially in the top surface of said screen, and the curved surface portions thereof are at least partly located in the bottom surface of said screen, whereby each of said openings has a pair of opposite walls formed by two adjacent wires of said one group, said walls being closest spaced from each other adjacent said top surface, and diverging from the area of closest spacing toward said bottom surface; and means for passing electric current through said wires so as to heat the same.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Apr. 12, 1949 

